Method of processing a gas stream



July 18, 1967 M. s. WORLEY METHOD OF PROCESSING A GAS STREAM originalFiled Feb. 19, 1964 /Wcw4 wr; J. War/ey INVENTOR BY/7 /d I @i afm/EnsUnited States Patent() 8 Claims. (Cl. 55-62) This application is adivision of application S.N. 345,- 942, tiled Feb. 19, 1964, and nowabandoned.

The present invention relates generally to a process for removing acidgas from a hydrocarbon fluid stream and recovering desirablehydrocarbons. Specifically the present invention relates to a processfor removing acid gas from a hydrocarbon fluid stream and recovering thedesirable hydrocarbons removed from the stream incidental to the acidgas removal.

Prior to the present invention both absorption and chemical reactionprocesses have been used for the removal of acid gases such as hydrogensulfide and carbon dioxide from a hydrocarbon fluid stream such as anatural gas well-stream. In a chemical reaction process such as onewhich includes the intimate contacting of the gas stream withmonoethanolamine or diethanolamine, considerable additional expense,both in intitial equipment and operating costs, is required as comparedto an absorption system. The chemical reaction type of process mentionedabove does not remove the desirable hydrocarbons from the iiuid streambeing processed. In many of the absorption processes of the prior art asubstantial amount of the hydrocarbons will be absorbed in the systemand in all such processes, these absorbed hydrocarbons are lost in theregeneration of the liquid absorbent. In most cases the quantity ofethane and heavier hydrocarbons absorbed is so great that the absorptionprocess becomes uneconomical for removing the acid gases. In othercases, the quantity of ethane and heavier hydrocarbons absorbed is muchless but still of such a magnitude as to contaminate the dischargedhydrogen sullide so that it cannot be used for making elemental sulfurby the most economical methods, Without further treatment. It is wellknown in the prior art that certain solid type adsorbents will besuitable for the processing of a hydrocarbon uid stream for the removalof desirable hydrocarbon -fractions but such adsorbents will noteconomically remove any substantial amount of the acid gases present inthe hydrocarbon uid stream being processed.

An object of the present invention is to provide a process for theremoval of acid gas from a hydrocarbon uid stream and for the recoveryof desirable hydrocarbons from such stream.

A further object of the present invention is to provide a combinationabsorption and adsorption process for the removal of acid gas from andfor the recovery of desirable hydrocarbons from a hydrocarbon fluidstream.

Another object of the present invention is to remove acid gases from ahydrocarbon fluid stream by absorption having a minimum amount of thesoluble hydrocarbon components in the removed acid gases.

Another object of the present invention is to recover a substantiallypure acid gas component from a natural gas stream containing a lighthydrocarbon gas component, a heavier hydrocarbon gas component and anacid gas component.

Still another object of the present invention is to provide anabsorption process for removal of acid gases from a hydrocarbon fluidstream in which hydrocarbon components which are soluble in theabsorption liquid are adsorbed from the stream prior to the absorptionof the acid gases from the stream.

A still further object of the present invention is to provide a processfor the recovery of desirable heavier hydrocarbons from a hydrocarbonfluid stream by adsorption and the further processing of the stream byabsorption to remove acid gas therefrom.

These and other objects of the present invention are more fullyexplained and discussed hereinafter with reference t`o the drawingswherein:

The drawing is a schematic ow diagram of one form of the process of thepresent invention.

Referring more in detail to the drawing:

A natural gas stream which is to be processed by the system of thepresent invention as illustrated in the drawing is conducted throughline 1 to valves 2 and 3. This gas stream will contain some acid gas andsome hydrocarbon gases, such as methane, ethane, propane, butane and thepentanes and heavier hydrocarbons. It is desired to remove the heavierhydrocarbons such as propane and heavier from the gas stream and toremove the acid gas from the gas stream leaving a gas stream composedsubstantially of methane and ethane. Valve 2 is connected into adsorbertower 4 and valve 3 is connected into adsorber tower 5. Towers 4 and 5-are filled with a solid adsorbent material which will adsorb thepropanes and heavier hydrocarbons and in some cases any water vaporpresent in the gas stream but will not adsorb any substantial quantitiesof acid gases present in the stream. It should be noted that while onlytwo towers 4 and 5 are shown any number of adsorber towers may be usedto adapt to the economy of processing the size and content of thenatural gas stream. Normally, to maintain continuous operations two ormore towers will be used. Adsorbent materials commonly used for theadsorption of propane and heavier hydrocarbons from natural gas streamssuch as sova beads, activated alumina, silica gel or charcoal are thematerials whose use is contemplated by the present invention. As shownin the drawing valve 2 is open and valve 3 is closed so that the gasstream is conducted through tower 4. Valves 6 and 7 connect into theoutlet connections from towers 4 and 5 respectively. With valve 2 open,valve 6 will be open to conduct the gas stream from tower 4 tocontacting vessel 8. The gas stream flowing into contacting vessel 8through inlet 9 will be substantially free of the propanes and heavierhydrocarbons. While the gas stream is owing through tower 4, tower 5will be in the process of being regenerated, as hereinafter more fullyexplained, to remove the adsorbed components from the adsorbent materialand to recover the heaviest of these components.

Within contacting vessel 8 the gas stream iiows upwardly and isintimately contacted with a suitable liquid absorbent in a plurality ofstages (not shown). Generally, any suitable type of contacting devicesuch as bubble trays or packing may be used to provide an intimatecounter-current contact between the gas stream and the liquid absorbent.The liquid absorbent is introduced into contacting vessel 8 throughupper liquid absorbent inlet 10 and intermediate liquid absorbent inlet11. The gas stream after being thoroughly contacted by the liquidabsorbent within contacting vessel S to remove the acid gas therefrom isdischarged from the upper part of vessel 8 through gas outlet 12 and isconducted through pressure reducing valve 13 to line 14. The liquidabsorbent used to contact the gas stream in contacting vessel 8 iscarefully selected to have a substantial capacity for absorbing theparticular acid gas or gases contained in the gas stream. Many liquidabsorbents such as the polybasic aliphatic alcohols, their ethers,esters and ether esters have a high capacity for absorption of acidgases generally present in natural gas streams but have not been usedpreviously in such applications because they also have a substantialcapacity for the absorption of the propane and heavier components of thenatural gas stream. With these components removed prior to theabsorption the most economical absorbent liquid may be used withoutcontamination of the acid gases or loss of the desirable heavierhydrocarbon components of the natural gas stream. The gas leaving thesystem of the present invention will have a minimum amount of acid gaspresent and will be substantially free of the propanes and other heavierhydrocarbons.

In some applications of the present invention it may be desirable thatthe gas used for regeneration of the adsorbent in towers 4 and 5 betaken from the inlet 9 and in such applications the pressure reducingvalve 13 will therefore be positioned in inlet 9 rather than gas outlet14.

The liquid absorbent collecting in the lower portion of contactingvessel 8 is discharged therefrom through liquid outlet 15 and tiowsthrough valve 16 into flash separator 17. Value 16 is responsive toliquid level controller 18 which maintains a proper level of liquidwithin the lower portion of contacting vessel 8 to prevent the dischargeof gas with the discharge of the liquids from contacting vessel 8. Thepressure on the liquids flowing through valve 16 is reduced so that thepressure Within ash separator 17 is substantially less than the pressurewithin contacting vessel 8. For example, assuming that contacting vessel8 is operating at a pressure of 1000 pounds per square inch then flashseparator 17 will operate at approximately 500 pounds per square inch.The vapors ashed from the liquid by the pressure reduction will beseparated and discharged from Hash separator 17 through vapor outlet 19.These vapors, because of their reduced pressure are pumped by pump 20through line 21 back into the lower portion of contacting vessel 8.These vapors will be substantially only methane and ethane with smallquantities of the acid gas. Their return to contacting vessel 8 willminimize the loss of methane and ethane by absorption. The acid gaswhich is returned to contacting vessel 8 from flash separator 17 will beabsorbed again by the liquid absorbent. If desired, however, the flashgases from ash separator 17 may be used to provide pneumatic power forthe process components and fuel for combustion to supply heat to theprocess. An economic balance must be made to determine the value ofthese flash gases if returned to contacting vessel 8 considering thecost of recompression as compared to their value as a source ofpneumatic power and fuel. The liquids are discharged from flashseparator 17 through liquid outlet 22 and are conducted through valve 23and heat exchanger 24, into flash separator 25. Valve 23 is controlledby liquid level controller 26.

The liquid discharged into Hash separator 25 may have been heated andwill lhave been subject to a pressure reduction through valve 23 wherebya substantial portion of the acid gas absorbed by the liquid absorbentwill be vaporized. The acid gas vapors are separated from the liquidabsorbent in ash separator 25 and are discharged through vapor outlet27. The liquid absorbent is discharged from ash separator 25 throughliquid outlet 28 and a portion of the liquid absorbent may be conductedto pump 29 for introduction into contacting vessel through intermediateliquid absorbent inlet 11. The remaining portion of the liquid absorbentdischarged from ash separator 25 is conducted through heat exchanger 30and heater 31 into the upper portion of stripping vessel 32. In largeunits the liquid from conduits 22 and 28 may be passed through turbinesfor power to pump regenerated liquid from conduit 33 into tower 8. Asweet gas stream is conducted through line 31a and heater 31 into thelower portion of stripping vessel 32. Within stripping vessel 32 acounter-current contact is achieved between the warm sweet gas and theheated partially regenerated absorbent liquid. The reconcentrated liquidabsorbent is discharged from stripping vessel 32 through liquid outlet33 and is pumped by pump 34 through heat exchanger 30 and heat exchanger24 or bypass 35 and valve 36 into contacting vessel 8 through upperliquid absorbent inlet 10. The gas stream is discharged from strippingvessel 32 through gas outlet 32a together with the acid gas which wasstripped from the liquid absorbent within stripping vessel 32.

It should be noted that in certain installations one or more of thefollowing listed elements of the previously described process may beeliminated without departing from the spirit of the present invention ifconditions such as degree of regeneration of the absorbent liquiddesired, the cost of the individual elements and their relativecontribution to the results of the processing of the gas stream: flashseparator 17, pump 20, heat exchangers 24 and 30, flash separator 25,pump 29, heater 31 and stripping vessel 32. Obviously, all of theaforementioned elements may not be eliminated unless some other suitableliquid absorbent regeneration means is substituted therefor. Factorssuch as the concentration of the acid gases, the absorption pressure,the degree of reconcentration of liquid absorbent needed, the desiredmaximum acid gas content in the outlet gas stream, the costs ofequipment and operations and numerous other factors must be consideredbefore eliminating items or substituting other equipment.

The regeneration of tower 5 as previously mentioned will be in processwhile the gas stream is flowing through tower 4. The regeneration gasflows from gas outlet 12 from contacting vessel 8 at a point ahead ofpressure reducing valve 13 and is conducted through heater 37 to valves38 and 39. While not shown 4heater 37 and heater 31 may be the sameheater if economies can be eiected in the heat requirements. Valve 38 isconnected to the inlet of tower 4 and valve 39 is connected to the inletof tower 5. With tower 4 processing the gas stream valve 38 will beclosed and valve 39 will be open to allow the hot regeneration gas toflow through tower 5. In flowing through tower 5 the hot regenerationgas will vaporize the components of the gas stream which have beenpreviously adsorbed therein when tower 5 was processing the gas stream.The regeneration gas stream will then flow from tower 5 through valve 40into line 41. Valve 42 which controls the flow from tower 4 to line 41will be closed. The regeneration gas stream flows through cooler 43 intoseparator 44. Sucient cooling should be available in cooler 43 tocondense substantially all of the desired heavier hydrocarbons whichwere absorbed in tower 5. These condensed hydrocarbons are separated-from the regeneration gas stream in separator 44 and are dischargedtherefrom through liquid outlet 45 to a suitable storage area (notshown) or other processing. In some processes it is desirable that theheavier hydrocarbons be retained in the natural gas stream after theacid gases have been removed. In such cases the cooling of cooler 43 maybe set so that only water and the heaviest of hydrocarbons will condenseand be discharged through outlet 45 from separator 44. If desiredseparator 44 may in some cases be omitted and the regeneration gasstream conducted directly from cooler 43 to line 14 with cooler 43providing su'icient cooling to prevent the temperature `of gas owingthrough line 14 from exceeding the temperature specied therefor. In thisway all of the hydrocarbons originally separated will be returned to thenatural gas stream after the acid gases have been removed and theremoval of the acid gases is not cornplicated by the presence of theheavier hydrocarbons. The regeneration gas is discharged from separator44 through outlet 46 and is conducted back into line 14 at a pointdownstream of pressure reducing valve 13. Generally, the operation ofpressure reducing valve 13 is controlled by a flow controller (notshown) positioned in the regeneration gas stream so that suicientpressure drop across valve 13 is maintained to provide adequate ow ofregeneration gas for the regeneration of towers 4 and 5.

Also, the operation of the regeneration gas stream can be controlled sothat if a particular heating or caloriiic value is required in the gasstream flowing out of the system through line 14 that suiiicientportions of propane or other hydrocarbons can be retained in theregeneration gas stream leaving separator 44. This may 4be accomplishedby controlling the temperature of the regeneration gas stream enteringseparator 44 whereby all of the propanes are not condensed. Adjustmentsof this temperature may be readily acc-omplished by control of cooler 43or by providing a by-pass (not shown) around cooler 43 whereby theaggregate temperature of the regeneration gas entering separator 44 isnot sufliciently cold to condense all of the propanes. The compositionof heavier hydrocarbons leaving separator 44 can also be adjusted by theselection of the adsorbent material and the design details of theadsorption equipment.

The heating of the regeneration gas stream is accomplished in heater 37but when the tower being regenerated is sutiiciently free of theadsorbed components from the gas stream then it is desired to cool theadsorbent material within the tower. This is accomplished by causing theregeneration gas stream to ow through heater by-pass line 47. Valves 48.and 49 are provided to control the flow of the regeneration gas so thatit will either ow through heater 37 or through line 47 in accordancewith the condition of the tower being regenerated. With valve 48 openand valve 49 closed all of the flow of the regeneration gas will bethrough heater 37 and the tower which is on regeneration willbereceiving heated regeneration gas. When valve 49 is open and valve 48 isclosed then all of the regeneration gas will be flowing through by-passline 47 and the tower on regeneration will be receiving coolregeneration gas to cool the reactivated adsorbent material within thetower.

Other types of regenerating systems are well known and may be usedwithout departing from the spirit of the invention. For example, theregeneration lgas can be a part of the natural gas stream. In .an opentype regeneration system the gas should be returned to a suitable placein the system. Care should be taken in using gas from these sources thatthe pressure in the regeneration system is maintained at the desiredlevel.

The regeneration gas may be taken from any other appropriate sourcewithout departing from the scope of the present invention. In some casesthe adsorbent material required may be charcoal and with this typesystem a steam type regeneration would be used.

In the Iform of the present invention shown in the drawing the gasstream is initially passed through an adsorption zone wherein theheavier hydrocarbon cornponents are removed from the stream byadsorption and later recovered in the regeneration of the adsorptionzone and then the stream is passed through an absorption zone whereinthe acid gases are absorbed from the stream by the absorbent liquid andare thereafter separated from the absorbent liquid in the absorbentliquid regeneration. By proper selection of both the adsorbent materialand the absorbent liquid the recovered hydrocarbons and the denuded gasstream will be substantially free of the acid gases and the acid gasesrecovered will be free of any appreciable amount of hydrocarboncontaminants. The hydrocarbons may be recovered in liquid state orreturned to the denuded gas stream. Where the acid gas recovered ishydrogen sulphide it will be in a suitable state and sufficiently freeof contaminants for ready conversion into free sulfur by well knownmethods.

The foregoing disclosure and description of the invention isillustrative and explanatory thereof, and various changes in the size,shape and materials, as well as in the details of the illustratedconstruction, may be made within the scope of the appended claimswithout departing from the spirit of the invention.

What I claim is: 1. The method of processing a natural gas streamcontaining a light hydrocarbon gas component, a heavier hydrocarbon gascomponent and an acid gas component to recover a substantially pure acidgas component including the steps of, iirst adsorbing substantially onlythe heavier hydrocarbon gas component from said natural gas stream in anabsorption zone, thereafter absorbing the acid gas component from saidlight hydrocarbon gas component in an absorbent liquid having an ainityfor adsorbing acid gas and heavier hydrocarbon gases to produce a gasstream containing substantially only said light hydrocarbon gascomponent, iiowing a regeneration gas stream of said light hydrocarbongas component through said adsorption zone to remove the adsorbedheavier hydrocarbon gas components from said adsorption zone, and

combining said lregeneration gas stream having the heavier hydrocarbongas component therein with said light hydrocarbon gas stream afterremoval of said acid -gas component.

2. The method according to claim 1, including the step of withdrawingsaid regeneration gas stream from said natural gas stream.

3. The method according to claim 1, including the step of withdrawingsaid regeneration gas stream from said lighter hydrocarbon gas stream.

4. The method according to claim 1, including the step of cooling theregeneration gas stream and said heavier hydrocarbon gas component priorto said combining step.

5. The method according to claim 4, including the step of removing theheavier hydrocarbon liquids condensed from said regeneration gas streamby said cooling step prior to said combining step.

6. The method according to calim 5, including the step of controllingthe amount of cooling of said regeneration gas stream and said heavierhydrocarbon gas component to maintain in the gaseous phase all of thoseheavier hydrocarbons which are desired to be combined with said lighterhydrocarbon gas component.

7. The method according to claim 3, including heating said regenerationgas stream before said owing step,

cooling said regeneration gas stream after said flowing step and beforesaid combining step,

restricting the iow of said lighter hydrocarbon gas stream downstream ofthe point of withdrawal of said regeneration gas stream and upstream ofthe point of combining said regeneration gas stream with said lighthydrocarbon gas component to create sufticient pressure drop for thedesired flow of regeneration gas.

8. The method of adsorbing an acid gas component from a natural gasstream containing a light hydrocarbon gas component, a heavierhydrocarbon gas component and an acid gas component with an adsorbentliquid having an -ainity for adsorbing both the acid gas component andthe heavier hydrocarbon gas component to recover a substantially pureacid gas component comprising,

first adsorbing substantially only the heavier hydrocarbon gas componentfrom said natural gas stream in an adsorption zone,

thereafter adsorbing with said adsorbent liquid having an affinity foradsorbing both said acid gas component and said heavier hydrocarbon gascomponent,

substantially only the acid gas component from said light ihydrocarbongas component to produce a gas stream containing substantially only saidlight hydrocarbon ygas component,

flowing a regeneration gas stream of said light hydrocarbon gascomponent through said adsorption zone to remove the adsorbed heavierhydrocarbons from said adsorption zone, and

combining said regeneration gas stream having the heavier hydrocarbongas component therein with the light hydrocarbon gas stream afterremoval of said acid gas component.

8 References Cited UNITED STATES PATENTS 2,982,721 5/1961 Dow 55-51 53,161,461 12/1964 Deal et al. 23--3 FOREIGN PATENTS 728,444 4/ 1955Great Britain.

REUBEN FRIEDMAN, Primary Examiner.

10 C. M. HART, Assistant Examiner.

1. THE METHOD OF PROCESSING A NATURAL GAS STREAM CONTAINING A LIGHTHYDROCARBON GAS COMPONENT, A HEAVIER HYDROCARBON GAS COMPONENT AND ANACID GAS COMPONENT TO RECOVER A SUBSTANTIALLY PURE ACID GAS COMPONENTINCLUDING THE STEPS OF, FIRST ABSORBING SUBSTANTIALLY ONLY THE HEAVIERHYDROCARBON GAS COMPONENT FROM SAID NATURAL GAS STREAM IN AN ABSORPTIONZONE, THEREAFTER ABSORBING THE ACID GAS COMPONENT FROM SAID LIGHTHYDROCARBON GAS COMPONENT IN AN ABSORBENT LIQUID HAVING AN AFFINITY FORABSORBING ACID GAS AND HEAVIER HYDROCARBON GASES TO PRODUCE A GAS STREAMCONTAINING SUBSTANTIALLY ONLY SAID LIGHT HYDROCARBON GAS COMPONENT,FLOWING A REGENERATION GAS STREAM OF SAID LIGHT HYDROCARBON GASCOMPONENT THROUGH SAID ADSORPTION ZONE TO REMOVE THE ADSORBED HEAVIERHYDROCARBON GAS COMPONENTS FROM SAID ADSORPTION ZONE, AND COMBINING SAIDREGENERATION GAS STREAM HAVING THE HEAVIER HYDROCARBON GAS COMPONENETTHEREIN WITH SAID LIGHT HYDROCARBON GAS STREAM AFTER REMOVAL OF SAIDACID GAS COMPONENET.